我正在尝试创建一个应用程序，该应用程序要求用户在被允许进入应用程序的其余部分之前成功输入一个pin。
我做了一些搜索，发现了一个基本的现有的CordaDa示例应用程序，工作在here。
我进入xcdatamodel，删除了它们的属性，并用“pin”替换，后者是一个字符串。这是xcdatamodel的截图。
然后我修改了ViewController，以便createData ui按钮打开一个alertController，提示用户输入两次新的pin，检查它们是否相同，如果相同，则使用该pin创建一个coredata条目。
以下是ViewController的相关代码：
import UIKit
import CoreData
class ViewController: UIViewController {
var firstPinNumber:String = ""
var secondPinNumber:String = ""
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
@IBAction func createData(_ sender: Any) {
let enterPinAlertController = UIAlertController(title: "Enter New PIN", message: "", preferredStyle: .alert)
enterPinAlertController.addTextField{ (textField1:UITextField)->Void in
textField1.placeholder = "Enter PIN"
textField1.isSecureTextEntry = true
}
enterPinAlertController.addTextField{ (textField2:UITextField)->Void in
textField2.placeholder = "Re-Enter PIN"
textField2.isSecureTextEntry = true
}
let okAction = UIAlertAction(title: "OK", style: .cancel) {(action) in
if let textFields = enterPinAlertController.textFields {
let theTextFields = textFields as [UITextField]
self.firstPinNumber = theTextFields[0].text!
self.secondPinNumber = theTextFields[1].text!
if self.firstPinNumber != self.secondPinNumber {
print ("PINs dont match!")
let pinsDontMatchAlertController = UIAlertController(title: "PINs don't match!", message: "Try again", preferredStyle: .alert)
let okAction = UIAlertAction(title: "OK", style: .cancel) {(action) in
}
pinsDontMatchAlertController.addAction(okAction)
self.present(pinsDontMatchAlertController, animated: true, completion: nil)
}
}
}
enterPinAlertController.addAction(okAction)
self.present(enterPinAlertController, animated: true, completion: nil)
createPIN(pinNum: secondPinNumber)
}
func createPIN(pinNum: String){
//As we know that container is set up in the AppDelegates so we need to refer that container.
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
//We need to create a context from this container
let managedContext = appDelegate.persistentContainer.viewContext
//Now let’s create an entity and new user records.
let userEntity = NSEntityDescription.entity(forEntityName: "User", in: managedContext)!
let user = NSManagedObject(entity: userEntity, insertInto: managedContext)
user.setValue(pinNum, forKeyPath: "pin")
print(user.value(forKey: "pin") as Any)
//Now we have set the pin. The next step is to save it inside the Core Data
do {
try managedContext.save()
} catch let error as NSError {
print("Could not save. \(error), \(error.userInfo)")
}
}
@IBAction func retrieveData(_ sender: Any) {
let storedPin = retrievePIN()
print(storedPin)
}
func retrievePIN()->String {
var storedPin:String = ""
//As we know that container is set up in the AppDelegates so we need to refer that container.
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return "" }
//We need to create a context from this container
let managedContext = appDelegate.persistentContainer.viewContext
//Prepare the request of type NSFetchRequest for the entity
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "User")
fetchRequest.fetchLimit = 1
// fetchRequest.predicate = NSPredicate(format: "username = %@", "Ankur")
// fetchRequest.sortDescriptors = [NSSortDescriptor.init(key: "email", ascending: false)]
//
do {
let result = try managedContext.fetch(fetchRequest)
for data in result as! [NSManagedObject] {
if data.value(forKey: "pin") != nil {
storedPin = data.value(forKey: "pin") as! String
print(storedPin)
} else {
print ("Found nil")
}
}
} catch {
print("Failed")
}
return storedPin
}
使用断点，我已经确定它进入了createPin（）函数，但它似乎在向enterPinAlertController显示输入新pin之前进入了该函数，即使在enterPinAlertController出现之后调用了createPin（）。
如果我使用retrieveData ui按钮，它会打印出“find nil”
所以，如果我的想法是正确的，那就是创建一个带有空字符串的coredata条目，或者什么都没有？
如何修复此问题，以便它使用用户作为新pin输入的字符串创建coredata条目，并在以后检索它？
最佳答案
您对createPin的调用需要在okAction的操作处理程序中。正如您现在所拥有的，将在显示警报之前调用secondPinNumber，因此它将是空的或nil，这取决于您初始化它的方式。
IBAction func createData(_ sender: Any) {
let enterPinAlertController = UIAlertController(title: "Enter New PIN", message: "", preferredStyle: .alert)
enterPinAlertController.addTextField{ (textField1:UITextField)->Void in
textField1.placeholder = "Enter PIN"
textField1.isSecureTextEntry = true
}
enterPinAlertController.addTextField{ (textField2:UITextField)->Void in
textField2.placeholder = "Re-Enter PIN"
textField2.isSecureTextEntry = true
}
let okAction = UIAlertAction(title: "OK", style: .cancel) {(action) in
if let textFields = enterPinAlertController.textFields,
let firstPinNumber = textFields[0].text,
let secondPinNumber = textFields[1].text,
firstPinNumber == secondPinNumber {
createPIN(pinNum: secondPinNumber)
} else {
print ("PINs dont match!")
let pinsDontMatchAlertController = UIAlertController(title: "PINs don't match!", message: "Try again", preferredStyle: .alert)
let okAction = UIAlertAction(title: "OK", style: .cancel)
pinsDontMatchAlertController.addAction(okAction)
self.present(pinsDontMatchAlertController, animated: true, completion: nil)
}
}
}
enterPinAlertController.addAction(okAction)
self.present(enterPinAlertController, animated: true, completion: nil)
}
关于ios - 核心数据似乎没有保存，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/55174162/